What is the best way to animate the camera path?
Create a single path for all of the trajectory. On the camera use a Follow Path Constraint. select the Target path, check the Follow Curve box so the camera starys aligned with the path and animate the Offset value.



On frame 1 create a Keyframe at 0. Go to to frame 500, change the offset value so that the camera reaches point B and insert another keyframe. Move to frame 550 and don't alter the offset value and insert another keyframe.

Keep doing the same procedure until your camera reaches point D.





The graph for the camera movement in the Graph Editor shows how the camera starts at 0, picks up speed, decelerates to a stop and accelerates again... all of that because as default Blender uses Bezier interpolation.